Polymers Division,
National Institute of Standards and Technology, Gaithersburg, MD

Although it is
well known that an intimate relationship exists between vascularization and
bone formation during development and fracture healing, where new bone
formation is preceded by local vascularization, the cellular cues that lead to
increased or maintained vascularization of bone remain unclear.† Specifically,
it is not clear whether osteoblasts, osteocytes (OCY), and/or osteoclasts are
involved in the recruitment of new vasculature.† Since OCYs form extensive
interconnected cellular networks throughout the bone tissue and respond to a
variety of mechanical and chemical stimuli, they have been proposed to be the
mechano/chemostat cells of bone tissue.† Thus OCYs may play an important role
in vascular recruitment both with and without mechanical loading.† The
objective of this study was to examine the ability of OCYs subjected to various
physiologic stimuli to enhance angiogenesis in vitro.

All CM treated groups except
hypoxia CM showed increased cell proliferation compared to the control group.†
There was a trend of increased proliferation in the mechanically loaded CM groups
compared to the static CM group.† Capillary-like network formation was similar
in HMVECs cultured in control medium, static CM, and hypoxia CM. However,
HMVECs cultured in DHP or flow CM showed more extensive capillary-like network
formation compared to control media.

In this study we have demonstrated
the ability of OCYs to enhance proliferation and capillary-like network
formation of HMVECs in vitro. †A better understanding of the interactions
between OCYs and endothelial cells may lead to treatments that can enhance bone
formation.